Systems of Neuroscience test #3
Brainstem: Reticular formation- what is it, what does it do, what is it made of
3 main divisions Median column (raphe nuclei) Located next to the midline Serotonergic neurons Medial column (magnocellular red nucleus) Large cells Made of gigantocellular nucleus, pontine tegmental reticular nucleus, cuneiform and subcuneiform nuclei (tegmental nuclei) Lateral column (parvocellular reticular nucleus) Lateral to the medial column Visceral function Small cells
Control of movement
4 divisions in the control of motor movement: Spinal cord and brainstem circuits (lower motor neurons) Descending Systems (upper motor neurons) Basal Ganglia Cerebellum
Cranial Nerve VI
Abducens "Abduction is movement away from the mid-line of the body. ... abductor - a muscle that can act to cause an abduction movement at a joint is called an abductor. For example, the abductor pollicis longus muscle. to abduct (verb) - e.g. "he abducted his right arm up to shoulder height". Motor: Innervates lateral rectus muscle Central connection: abducens nucleus in the pons Exits at border between pons and medulla•Enters the subarachnoid space and pierces the dura mater to run in a space known as Dorello's canal. Travels through the cavernous sinus at the tip of the petrous temporal bone, before entering the orbit of the eye through the superior orbital fissure. Movement of eyeball
Control of amplitude and direction
Amplitude: encoded by duration of neuronal activity in the lower motor neurons After each saccade, reestablish baseline activity to hold the eye steady Direction is determined by which eye muscles are activated Not easy to separately control each muscle independently Controlled by local circuit neurons in two gaze centers
Damage to Abducens Nerve VI
Any pathology which leads to downward pressure on the brainstem (e.g. brain tumor, extradural hematoma) can lead to the nerve becoming stretched along the clivus of the skull. Wernicke-Korsakoff syndrome (caused by thiamine deficiency and generally seen in alcoholics) is a rare cause of sixth nerve palsy.•Other causes of abducens nerve damage include diabetic neuropathy•Patients will present with diplopia and a medially rotated eye which cannot be abducted past the midline. The patient may attempt to compensate by rotating their head to allow the eye to look sideways.
Frontal eye fields
Assorted areas of the frontal and parietal cortices, including the frontal eye fields (in frontal lobe rostral to premotor cortex) Frontal eye fields -> superior colliculus -> PPRF on contralateral side•Also to the vertical gaze center, but why make this more complicated?•So, frontal eye fields can control eye movements by activating upper motor neurons in the superior colliculus•Frontal eye fields PPRF on contralateral side •Can directly influence eye movements w/o the superior colliculus
What the superior colliculus is involved in/doing
Both the superior colliculus and frontal eye fields have a) upper motor neurons, and b) a topographical map of eye movement vectors have neurons that respond to auditory and somatosensory stimuli, and their location in space•
Brainstem: Reticular activating system- what is it, what does it do, what structures participate
Bulboreticular facilitory area Ignition system Prepares your brain for higher level of activity Neurons project upward and synapse on neurons in "non-specific" or "diffuse" thalamic nuclei. These nuclei send projections to all areas of the cerebral cortex. Continuous with regions of the thalamus and hypothalamus Reticular nucleus of the thalamus GABAergic neurons Does not project to cortex directly Modulates the rest of the thalamus and information flowing through it May help the organism respond to novel stimuli Lateral hypothalamic area Includes lateral hypothalamus, ventrolateral preoptic area Orexin system- arousal, wakefulness, appetite Bulboreticular facilitory area Ignition system Prepares your brain for higher level of activity Neurons project upward and synapse on neurons in "non-specific" or "diffuse" thalamic nuclei. These nuclei send projections to all areas of the cerebral cortex. Continuous with regions of the thalamus and hypothalamus Reticular nucleus of the thalamus GABAergic neurons Does not project to cortex directly Modulates the rest of the thalamus and information flowing through it May help the organism respond to novel stimuli Lateral hypothalamic area Includes lateral hypothalamus, ventrolateral preoptic area Orexin system- arousal, wakefulness, appetite
Brainstem: What makes up the tegmentum
Contains ascending and descending tracts; many relay nuclei, and the nuclei of cranial nerves III to X, and XII Includes the "tegmentum"- red nucleus and substantia nigra
What happens if you have damage to the frontal eye fields
Damage to frontal eye fields -> problems with saccades on side contralateral to the lesion Damage to frontal eye fields -> produce permanent deficits in ability to make saccades that are not guided by an external target Cannot voluntarily direct eyes away from a stimulus (anti-saccade)
Damage to superior colliculus
Damage to superior colliculus -> saccades still occur, but they may be slower/less accurate -> Suggests the frontal eye fields and the superior colliculus compensate and complement each other Do NOT have the same function Damage to superior colliculus -> permanent deficit in ability to perform express saccades Short-latency, reflex-like eye movements that are mediated by direct pathways from retina/visual cortex -> superior colliculus
Lower motor neuron syndrome
Damage to the lower motor neurons•Results in paralysis of the affected muscles•Loss of reflexes because sensorimotor reflex arcs are disrupted•Loss of muscle tone (muscle spindles no longer linked to a lower motor neuron)•Muscles may spontaneously twitch due to changes in excitability or due to pathological activity of the motor fiber•Can lead to muscular atrophy from disuse
Midbrain
Extends from pons to roughly the thalamus on the dorsal-ventral axis Extends from the caudal end of the mammillary bodies to the posterior commissure on the anterior-posterior axis Posterior aspect: characterized by the superior and inferior colliculi, and their respective nuclei Anterior aspect: characterized by the crus cerebri and interpeduncular fossa. Crus cerebri: anterior part of the cerebral peduncle; contains motor tracts coming from the cortex Interpeduncular fossa: houses oculomotor nucleus Fun fact: exists in primates, but does not appear to exist in rodents Cranial Nerves: oculomotor nerve (III, motor) exits the anterior aspect and the trochlear nerve (IV, motor) exits its posterior aspect
Cranial Nerve VII
Facial Sensory Portion: Innervates anterior 2/3 of tongue Central connection: nucleus solitarius (solitary nucleus) Taste Motor Portion: Innervates muscles of facial expression, stapedius muscle Central connection: facial nucleus Facial movement, tension on bones of middle ear Parasympathetic Portion Innervates salivary and lacrimal glands via submandibular and pterygopalatine ganglia Central connection: superior salivatory nucleus Salivation and lacrimation intracranial The nerve arises in the pons It begins as two roots; a large motor root, and a small sensory root. The two roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of the temporal bone. Here, they are in very close proximity to the inner ear. Still within the temporal bone, the roots leave the internal acoustic meatus, and enter into the facial canal. Intracranial Within the facial canal, three important events occur: Firstly the two roots fuse to form the facial nerve. Next, the nerve forms the geniculate ganglion, L-shaped collection of fibers and sensory neurons of the facial nerve. Lastly, the nerve gives rise to the greater petrosal nerve (parasympathetic fibers to glands), the nerve to stapedius (motor fibers to stapedius muscle), and the chorda tympani (special sensory fibers to the anterior 2/3 tongue). The facial nerve then exits the facial canal (and the cranium) via the stylomastoid foramen. This is an exit located just posterior to the styloid process of the temporal bone. Extracranial After exiting the skull, the facial nerve turns superiorly to run just anterior to the outer ear. The first extracranial branch to arise is the posterior auricular nerve. Provides motor innervation to the some of the muscles around the ear. The main trunk of the nerve, now termed the motor root of the facial nerve, continues anteriorly and inferiorly into the parotid (salivary) gland (note - the facial nerve does not contribute towards the innervation of the parotid gland). Within the parotid gland, the nerve terminates by splitting into five branches: Temporal branch Zygomatic branch Buccal branch Marginal mandibular branch Cervical branch These branches are responsible for innervating the muscles of facial expression.
Cranial Nerve IX
Glossopharyngeal One of the smallest cranial nerves Has many functional components: Taste Sensation from 1/3 of tongue Sensation from pharyngeal wall Sensation from carotid sinus (baroceptors/blood pressure) Sensation from external ear Branchiomotor innervation of the stylopharyngeus muscle (swallowing) Parasympathetic innervation to parotid gland (major salivary gland) Functional parts SVA (special visceral afferent)- taste Inferior glossopharyngeal ganglion (or solitary nucleus) GVA (general visceral afferent)- sensation from posterior tongue, pharyngeal wall, carotid sinus•Inferior glossopharyngeal ganglion GSA (general somatic afferent)- sensation from external ear Superior glossopharyngeal ganglion SVE (special visceral efferent)- branchiomotor to stylopharyngeus muscle Nucleus ambiguus GVE (general visceral efferent)- parasympathetic to parotid (salivary gland) Inferior salivatory nucleus The glossopharyngeal nerve originates in the medullaoblongata It emerges from the anterior aspect of the medulla, moving laterally in the posterior cranial fossa. The nerve leaves the cranium via the jugular foramen. At this point, the tympanicnerve arises. Sensory from middle ear and The glossopharyngeal nerve terminates by splitting into several sensory branches: Pharyngeal branch - combines with fibers of the vagus nerve to form the pharyngeal plexus. It innervates the mucosa of the oropharynx (middle part of throat behind mouth) Lingual branch - provides the posterior 1/3 of the tongue with general and taste sensation Tonsillar branch - forms a network of nerves, known as the tonsillar plexus, which innervates the palatine tonsils. Sensory (special sensory) Innervates posterior 1/3 of tongue, carotid body, carotid sinus Central connection: solitary nucleus Taste, chemoreception, baroreception Motor Innervates stylopharyngeus muscle (acts to shorten and widen the pharynx, and elevate the larynx during swallowing) Central connection: nucleus ambiguus Swallowing Parasympathetic Innervates parotid salivary gland via otic ganglion Central connection: inferior salivatory nucleus Salivation Supplies sensory innervation to the oropharynx, and thus carries the afferent information for the gag reflex. When a foreign object touches the back of the mouth, this stimulates CNIX, beginning the reflex. The efferent nerve in this process is the vagus nerve. An absent gag reflex signifies damage to the glossopharyngeal nerve.
Lateral and medial rectus muscles
Horizontal movements Medial rectus: adduction (toward the nose); controlled by oculomotor nerve (CNIII) Lateral rectus: abduction (away from the nose); controlled by abducens nerve (CNVI)
Cranial Nerve XII
Hypoglossal Motor Innervates intrinsic and extrinsic muscles of tongue Central connection: hypoglossal nucleus (medulla oblongata) Movement of tongue Passes laterally across the posterior cranial fossa, within the subarachnoid space. Exits the cranium via the hypoglossal canal. Now extracranial, the nerve receives a branch of the cervical plexus that conducts fibers from C1/C2 spinal nerve roots. They do not combine with the hypoglossal nerve - they merely travel within its sheath. It then passes inferiorly to the angle of the mandible, crossing the internal and external carotid arteries, and moving in an anterior direction to enter the tongue. Role of the C1/C2 Roots The C1/C2 roots that travel with the hypoglossal nerve also have a motor function. Branch off to innervate the geniohyoid (elevates the hyoid bone) and thryohyoid (depresses the hyoid bone) muscles. Another branch containing C1/C2 fibers descends to supply the ansa cervicalis - a loop of nerves that is part of the cervical plexus. From the ansa cervicalis, nerves arise to innervate the omohyoid, sternohyoid and sternthyroid muscles. These muscles all act to depress the hyoid bone. The hypoglossal nerve is examined by asking the patient to protrude their tongue. Other movements such as asking the patient to push their tongue against their cheek and feeling for the pressure on the opposite side of the cheek may also be used if damage is suspected. Patients will present with deviation of the tongue towards the damaged side on protrusion, as well as possible muscle wasting and fasciculations (twitching of isolated groups of muscle fibers) on the affected side.
Brainstem: What happens if you get damage to descending tracts
Internal capsule is particularly susceptible to compression from haemorrhagic bleeds, known as a 'capsular stroke'. Can result in a lesion of the descending tracts. Corticospinal Tracts Pyramidal tracts are susceptible to damage, because they extend almost the whole length of the CNS Particularly vulnerable as they pass through the internal capsule - a common site of cerebrovascular accidents Corticospinal Tracts I f there is only a unilateral lesion of the left or right corticospinal tract, symptoms will appear on the contralateral side of the body. Hypertonia - an increased muscle tone Hyperreflexia - increased muscle reflexes Clonus - involuntary, rhythmic muscle contractions Babinski sign - extension of the hallux (big toe) in response to blunt stimulation of the sole of the foot Muscle weakness Corticobulbar Tracts Bilateral nature of the majority of the corticobulbar tracts means a unilateral lesion usually results in mild muscle weakness. Not all the cranial nerves receive bilateral input, and so there are a few exceptions: Hypoglossal nerve - a lesion to the upper motor neurons -> spastic paralysis of the contralateral side/deviation of the tongue Facial nerve - a lesion to the upper motor neurons -> spastic paralysis of the muscles in the contralateral lower quadrant of the face Extrapyramidal Tracts Lesions are commonly seen in degenerative diseases, encephalitis, and tumors. They result in various types of dyskinesias (disorders of involuntary movement)
Damage to facial nerve VII
Intracranial Damage/Lesions The muscles of facial expression will be paralysed or severely weakened. The other symptoms produced depend on the location of the lesion, and the branches that are affected: Chorda tympani - reduced salivation and loss of taste on the ipsilateral 2/3 of the tongue. Nerve to stapedius - ipsilateral hyperacusis (hypersensitive to sound). Greater petrosal nerve - ipsilateral reduced lacrimal fluid production. The most common cause of an intracranial lesion of the facial nerve is middle ear pathology - such as a tumor or infection. If no definitive cause can be found, the disease is termed Bell's palsy Facial Extracranial Damage/Lesions Only the motor function of the facial nerve is affected, resulting in paralysis or severe weakness of the muscles of facial expression. There are various causes of extracranial lesions of the facial nerve: Parotid gland pathology - e.g a tumour, parotitis, surgery. Infection of the nerve- particularly by the herpes virus. Compression during forceps delivery - the neonatal mastoid process is not fully developed, and does not provide complete protection of the nerve. Idiopathic - If no definitive cause can be found, the disease is termed Bell's palsy.
Gaze centers: what are they, which ones are concerned with what (horizontal or vertical), what connects to them, where do they connect to
Located in the reticular formation Paramedian pontine reticular formation (PPRF): horizontal gaze center Collection of local circuit neurons near the midline of the pons Rostral interstitial nucleus/mesencephalic reticular formation: vertical gaze center Collection of local circuit neurons in the rostral part of the midbrain reticular formation Activation of each gaze center separately results in eye movements along that single axis Activation in concert results in oblique movements (not oblique muscle action, per se)
ALS
Neurogenerative disease•Slow, but progressive, loss of α motor neurons in the spinal cord and brainstem, as well as upper motor neurons in the cortex•Starts with progressive weakness•Muscles waste•Currently no effective treatment•Why? Genetics, reactive oxygen species, pro-inflammatory interactions between neurons and microglia, mitrochondrial dysfunction... •Leading current hypothesis is hyperexcitability in cortical networks which may lead to glutamate excitotoxicity
Cranial Nerve III
Oculomotor Motor: Innervates superior/inferior/medial rectus muscles (raises/depresses/adducts the eyeball), inferior oblique muscle (elevates, abducts and laterally rotates the eyeball) , levator palpebrae superioris muscle (raise upper eyelid) Central connection: oculomotor nucleus•Movement of eyeball, elevation of upper lid Originates from the anterior aspect of the midbrain. Moves anteriorly, passing below the posterior cerebral artery, and above the superior cerebellar artery. Pierces the dura mater and enters the lateral aspect of the cavernous sinus. The nerve leaves the cranial cavity via the superior orbital fissure. Divides into superior and inferior branches. Once within the orbital cavity, both branches innervate accessory structures of the eye: Superior branch: Motor innervation to the superior rectus and levator palpabrae superioris. Inferior branch: Motor innervation to the inferior rectus, medial rectus and inferior oblique. Parasympathetic fibers to the ciliary ganglion, which ultimately innervates the sphincter pupillae and ciliary muscles. Parasympathetic Innervates sphincter pupillae and ciliary muscle of the eyeball via ciliary ganglion Central connection: Edinger-Westphal nucleus (accessory oculomotor nucleus) Pupillary constriction and accommodation Originates from the anterior aspect of the midbrain. Moves anteriorly, passing below the posterior cerebral artery, and above the superior cerebellar artery. Pierces the dura mater and enters the lateral aspect of the cavernous sinus.
Cranial Nerve I
Olfactory Sensory: Olfaction Information collected in olfactory epithelium Fibers of olfactory neurons Central connection: olfactory bulb Shortest cranial nerve CN of telencephalon Olfactory receptor cells are bipolar nerve cells with a peripherally directed dendrite which terminates in a knob from which numerous cilia project.•The olfactory chemoreceptors are located on these cilia. Synapse on mitral cells of olfactory bulb•Olfactory tract: The lateral stria sends carries the axons to the primary olfactory cortex. The medial stria carry the axons across the medial plane of the anterior commissure where they meet the olfactory bulb of the opposite side. Unmyelinated, covered by olfactory Schwann cells (olfactory ensheathing glia) Nerve capable of regeneration•Information passed on to olfactory cortex and amygdala
Damage -> Inability to smell
Olfactory Cranial nerve I Age: the older you get, the less you can smell Possibly due to repeated damage and infections over time
Pons
One of the easiest structures to find, at least in part Basilar pons: round bit Pontine tegmentum: contains portions of several cranial nerves/nuclei "The pons (the metencephalon) extends from the pons-medulla junction to an imaginary line drawn from the exit of the trochlear nerve posteriorly to the rostral edge of the basilar pons anteriorly " (Fundamental Neurscience...) Portions of the trigeminal nuclei and the vestibular(cochlear) nuclei Right at the pons-medulla border: facial motor nucleus, superior salivatory nucleus (facial nerve), and abducens nucleus. Trigeminal nerve (V, mixed) emerges from the lateral aspect of the pons Abducens (VI, motor), facial (VII, mixed), and vestibulocochlear (VIII, sensory) nerves exit at the pons-medulla junction
Cranial Nerve II
Optic Sensory: Transmits information from retina Central connection: lateral geniculate nucleus, pretectal nucleus Vision, pupillary light reflex The other cranial nerve that does not join up with the brainstem CN of diencephalon Technically part of the CNS rather than the PNS because it is derived from an out-pouching of the diencephalon (optic stalks) during embryonic development. Due to its unique anatomical relation to the brain, the optic nerve is surrounded by cranial meninges (not by epi-, peri- and endoneurium like most other nerves) Olfactory nerve too Extracranial The optic nerve is formed by the convergence of axons from the retinal ganglion cells. Receive impulses from the photoreceptors of the eye (the rods and cones). The nerve leaves the bony orbit via the optic canal, a passageway through the sphenoid bone. It enters the cranial cavity, running along the surface of the middle cranial fossa (in close proximity to the pituitary gland). Intracranial Within the middle cranial fossa, the optic nerves from each eye unite to form the optic chiasm. At the chiasm, fibers from the nasal (medial) half of each retina cross over, forming the optic tracts So, optic nerve is before crossing, optic tract is after crossing
Damage to optic chiasm
Optic Cranial Nerve II Compression to the optic chiasm particularly affects the fibers that are crossing over from the nasal half of each retina. This produces visual defect affecting the peripheral vision in both eyes, known as a bitemporal hemianopia
What happens if an image is stagnant on the retina
Really inhibits your ability to visually perceive things•Stabilized retinal images: make sure the image always falls on exactly the same parts of the retina•Stabilized images rapidly disappear•Even when you are staring at a stationary image, your eyes are making slight movements, just fractions of a degree, to keep the image "fresh"
How does sensory information get incorporated
Sensory info comes in and leads to activation of neighboring upper motor neurons that will move the eye an appropriate amount to align the fovea to the target
Cranial Nerve XI
Spinal Accessory Motor Innervates sternomastoid and trapezius muscle Central connection: spinal cord Movement of head and shoulder Examined by asking the patient to rotate their head and shrug their shoulders, both normally and against resistance. Originally believed to have two roots- cranial and spinal Turns out, the cranial root is actually mostly made of vagal nerve fibers The spinal root gets fibers from the spinal accessory nucleus of the ventral cervical spinal cord So, XI is not the most cranial Cranial nerve Spinal Portion Arises from neurons of the upper spinal cord (C1-C5/C6 spinal nerve root) Coalesce to form the spinal part of the accessory nerve, which then runs superiorly to enter the cranial cavity via the foramen magnum. Spinal Portion The nerve traverses the posterior cranial fossa to reach the jugular foramen. Briefly meets the cranial portion of the accessory nerve, before exiting the skull (along with the glossopharyngeal and vagus nerves). Outside the cranium, the spinal part descends along the internal carotid artery to reach the sternocleidomastoid muscle, which it innervates. It then moves across the posterior triangle of the neck to supply motor fibers to the trapezius. Cranial Part Much smaller, and arises from the lateral aspect of the medulla oblongata. Leaves the cranium via the jugular foramen, where it briefly contacts the spinal part of the accessory nerve. Cranial Part Immediately after leaving the skull, cranial part combines with the vagus nerve (CN X) at the inferior ganglion of vagus nerve (a ganglion is a collection of nerve cell bodies). The fibers from the cranial part are then distributed through the vagus nerve. For this reason, the cranial part of the accessory nerve is considered as part of the vagus nerve.
Brainstem: Corticospinal, corticobulbar- what are they, what info do they carry, know the pathway (where it starts, ends, synapses, crosses), know any subdivisions (like lateral and anterior corticospinal) The 4 corticobulbar tracts- names, do they cross, where do they start
The corticospinal tracts begin in the cerebral cortex, from which they receive a range of inputs: Primary motor cortex Premotor cortex Supplementary motor area They also receive nerve fibers from the somatosensory area Somatosensory area plays a role in regulating the activity of the tracts. Neurons converge and descend through the internal capsule Internal capsule: a white matter pathway, located between the thalamus and the basal ganglia Clinical importance: internal capsule is particularly susceptible to compression from haemorrhagic bleeds, known as a 'capsular stroke'. Can result in a lesion of the descending tracts. After the internal capsule, the neurons pass through the crus cerebri of the midbrain, the pons and into the medulla. In the most inferior (caudal) part of the medulla, the tract divides into two: The fibers within the lateral corticospinal tract mostly cross over to the other side of the CNS. Descend into the spinal cord, terminating in the ventral horn (at all segmental levels). From the ventral horn, the lower motor neurons go on to supply the muscles of the body. The anterior corticospinal tract remains ipsilateral, descending into the spinal cord. They then decussate and terminate in the ventral horn of the cervical and upper thoracic segmental levels. In the most inferior (caudal) part of the medulla, the tract divides into two: Lateral corticospinal tract: mostly limb control Anterior corticospinal tract: mostly trunk and shoulders Arise from the lateral aspect of the primary motor cortex. Receive the same inputs as the corticospinal tracts. Fibers pass through the internal capsule to the brainstem. The neurons terminate on the motor nuclei of the cranial nerves. Here, they synapse with lower motor neurons, which carry the motor signals to the muscles of the face and neck. Many of these fibers innervate the motor neurons bilaterally. Example: fibers from the left primary motor cortex act as upper motor neurons for the right and left trochlear nerves. There are a few exceptions to this rule: Upper motor neurons for the facial nerve (CN VII) have a contralateral innervation. This only affects the muscles in the lower quadrant of the face - below the eyes Upper motor neurons for the hypoglossal (CN XII) nerve only provide contralateral innervation.
Muscle Spindles
The large motor neurons that do most of the work: α motor neurons•Innervate the striated muscle fibers•Also have γ motor neurons•Innervate muscle spindles•Regulate the sensory input by setting the intrafusal muscle fibers to an appropriate length•Muscle spindle: specialized muscle fibers that do not contribute to the work•Also known as intrafusal fibers•Embedded within connective tissue capsules in the muscle•Innervated by sensory axons to relay information about the length of the muscle
damage to cranial nerve IV trochlear
The target is moved in an 'H-shape' and the patient is asked to report any blurring of vision or diplopia (double vision). Damage to the Trochlear Nerve The most common cause is congenital fourth nerve palsy, a condition of abnormal development. This may be curable with surgery. Other causes of trochlear nerve damage include diabetic neuropathy, thrombophlebitis of the cavernous sinus and raised intracranial pressure
Lower Motor Neurons
These are the motor neurons that live in your spinal cord or brainstem that transmit the motor message directly to the skeletal muscle •Where they synapse is known as the neuromuscular junction•Also known as α motor neurons•Those that control bodily musculature have their cell bodies in the ventral horn of the spinal cord and send their axons out through the ventral roots to join the spinal peripheral nerves•Those that control the head and neck have their cell bodies in the brainstem and send their axons out to join the cranial nerves Receive input from local circuit neurons. Local circuit neurons receive information from:•Sensory neurons•Important for sensorimotor reflexes•Descending pathways from "higher" centers•Upper motor neurons (cortex, brainstem)•The lower motor neuron serves as the final common pathway for transmitting to and controlling the muscles
Brainstem: Extrapyramidal tracts
These tracts originate in the brain stem, carrying motor fibers to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion
Brainstem: Pyramidal tracts
These tracts originate in the cerebral cortex, carrying motor fibers to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face.
Types of eye movements
Those that shift the direction of gaze Important for foveation Movements: vergence movements Those that stabilize the gaze Help maintain foveation while the head is moving Movements: saccades, smooth pursuit movements, and vestibulo-ocular and optokinetic movements
Cranial Nerve V
Trigeminal Sensory Portion: Innervates face, scalp, cornea, nasal cavity, oral cavity, cranial dura mater Central connection: trigeminal sensory nuclei•Three sensory nuclei (mesencephalic, principal sensory, spinal nuclei of trigeminal nerve) At the level of the pons, the sensory nuclei merge to form a sensory root Take up more CNS real estate than any other cranial nerve cell group General sensation Motor Portion Innervates muscles of mastication, tensor tympani Central connection: trigeminal motor nucleus At the level of the pons, the motor nucleus continues to form a motor root. The motor root passes inferiorly to the sensory root, along the floor of the trigeminal cave. Its fibers are only distributed to the mandibular division. Opening and closing mouth, tension on tympanic membrane In middle cranial fossa, the sensory root expands into the trigeminal ganglion. The trigeminal ganglion is located lateral to the cavernous sinus, in a depression of the temporal bone (trigeminal cave) The peripheral aspect of the trigeminal ganglion gives rise to 3 divisions: ophthalmic (V1), maxillary(V2) and mandibular (V3). Ophthalmic Nerve (V1) Gives rise to 3 terminal branches: frontal, lacrimal and nasociliary, which innervate the skin and mucous membrane of derivatives of the frontonasal prominence derivatives: Forehead and scalp Frontal and ethmoidal sinus Upper eyelid and its conjunctiva•Cornea (see clinical relevance) Dorsum of the nose The corneal reflex is the involuntary blinking of the eyelids - stimulated by tactile, thermal or painful stimulation of the cornea. In the corneal reflex, the ophthalmic nerve (V1) acts as the afferent - detecting the stimuli. The facial nerve is the efferent limb, causing contraction of the orbicularis oculi muscle. If the corneal reflex is absent, it is a sign of damage to the trigeminal/ophthalmic nerve, or the facial nerve. Maxillary Nerve (V2) Maxillary nerve gives rise to 14 terminal branches, which innervate the skin, mucous membranes and sinuses of derivatives of the maxillary prominence of the 1st pharyngeal arch: Lower eyelid and its conjunctiva Cheeks and maxillary sinus Nasal cavity and lateral nose Upper lip Upper molar, incisor and canine teeth and the associated gingiva Superior palate Mandibular Nerve Mandibular nerve gives rise to four terminal branches in the infra-temporal fossa: buccal nerve, inferior alveolar nerve, auricotemporal nerve and lingual nerve. These branches innervate the skin, mucous membrane and striated muscle derivatives of the mandibular prominence of the 1st pharyngeal arch. Sensory supply: Mucous membranes and floor of the oral cavity External ear Lower lip Chin Anterior 2/3 of the tongue (only general sensation; special taste sensation supplied by the chorda tympani, a branch of the facial nerve) Lower molar, incisor and canine teeth and the associated gingiva Motor Supply: Muscles of mastication; medial pterygoid, lateral pterygoid, masseter, temporalis Anterior belly of the digastric muscle and the mylohyoid muscle (these are suprahyoid muscles) Tensor veli palatini Tensor tympani
Cranial Nerve IV
Trochlear Motor: Innervates a single muscle, the superior oblique muscle A muscle of oculomotion. As the fibers from the trochlear nucleus cross in the midbrain before they exit, the trochlear neurons innervate the contralateral superior oblique. Central connection: trochlear nucleus Movement of eyeball Fewest axons, but longest intracranial axon path Only CN to emerge from dorsal aspect of midbrain/brainstem Only CN to cross the midline Arises from the trochlear nucleus of the brain, emerging from the posterior aspect of the midbrain Only cranial nerve to exit from the posterior midbrain It runs anteriorly and inferiorly within the subarachnoidspace before piercing the dura mater adjacent to the posterior clinoid process of the sphenoid bone. The nerve then moves along the lateral wall of the cavernous sinus (along with the oculomotor nerve, the abducens nerve, the ophthalmic and maxillary branches of the trigeminal nerve and the internal carotid artery) before entering the orbit of the eye via the superior orbital fissure. Origin and distribution of the trochlear nerve (cranial nerve IV) to the superior oblique muscle. As indicated in the cross section of the brainstem, note that this nerve exits the brain from the dorsal aspect, and it is the only nerve that is crossed. Arrow indicates direction of movement of the bulb downward and inward. Examination of the Trochlear Nerve Examined in conjunction with the oculomotor and abducens nerves by testing the movements of the eye. Patient is asked to follow a point with their eyes without moving their head. The target is moved in an 'H-shape' and the patient is asked to report any blurring of vision or diplopia (double vision). Damage to the Trochlear Nerve The most common cause is congenital fourth nerve palsy, a condition of abnormal development. This may be curable with surgery. Other causes of trochlear nerve damage include diabetic neuropathy, thrombophlebitis of the cavernous sinus and raised intracranial pressure
Brainstem: The two slides on Spinocerebellar Tracts
Unconscious sensation The tracts that carry unconscious proprioceptive information are collectively known as the spinocerebellar tracts. Although we cannot physically acknowledge these signals, they help our brain coordinate and refine motor movements. They transmit information from the muscles to the cerebellum. There are four individual pathways: Posterior Spinocerebellar tract - Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum. Cuneocerebellar tract - Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum. Anterior spinocerebellar tract - Carries proprioceptive information from the lower limbs. Fibers decussate twice - and so terminate in the ipsilateral cerebellum. Rostral spinocerebellar tract - Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum.
Cranial Nerve X
Vagus Large nerve Has the most extensive distribution in the body of all cranial nerves Innervates all the way down into the abdomen Also has 5 functional components like the glossopharyngeal nerve (SVA, GVA, GSA, SVE, GVE)•2 rootlets that originate from the brain and join together In the Head Originates from the medulla of the brainstem. Exits the cranium via the jugular foramen, with the glossopharyngeal and accessory nerves (CN IX and XI respectively). Within the cranium, the auricular branch arises. This supplies sensation to the posterior part of the external auditory and canal external ear. In the Neck Passes into the carotid sheath, travelling inferiorly with the internal jugular vein and common carotid artery. At the base of the neck, the right and left nerves have differing pathways: The right vagus nerve passes anterior to the subclavian artery and posterior to the sternoclavicular joint, entering the thorax. The left vagus nerve passes inferiorly between the left common carotid and left subclavian arteries, posterior to the sternoclavicular joint, entering the thorax. Several branches arise in the neck: Pharyngeal branches - Provides motor innervation to the majority of the muscles of the pharynx and soft palate. Superior laryngeal nerve - Splits into internal and external branches. The external laryngeal nerve innervates the cricothyroid muscle of the larynx. The internal laryngeal provides sensory innervation to the laryngopharynx and superior part of the larynx. Recurrent laryngeal nerve (right side only) - Hooks underneath the right subclavian artery, then ascends towards to the larynx. It innervates the majority of the intrinsic muscles of the larynx. In the Thorax The right vagus nerve forms the posterior vagal trunk, the left forms the anterior vagal trunk. Branches from the vagal trunks contribute to the formation of the oesophageal plexus, which innervates the smooth muscle of the oesophagus. Two other branches arise in the thorax: Left recurrent laryngeal nerve - hooks under the arch of the aorta, ascending to innervate the majority of the intrinsic muscles of the larynx. Cardiac branches - these innervate regulate heart rate and provide visceral sensation to the organ. The vagal trunks enter the abdomen via the oesophageal hiatus, (opening in the diaphragm)In the Abdomen In the abdomen, the vagal trunks terminate by dividing into branches that supply the oesophagus, stomach and the small and large bowel (up to the splenic flexure). Sensory Innervates pharynx, larynx, trachea, esophagus, external ear Central connection: trigeminal sensory nucleus General sensation Sensory (special sensory) Innervates thoracic and abdominal viscera, aortic bodies, aortic arch Central connection: solitary nucleus•Visceral sensation, chemoreception, baroreception Motor Innervates soft palate, pharynx, larynx, upper esophagus Central connection: nucleus amibiguus Speech, swallowing Parasympathetic Innervates thoracic and abdominal viscera Central connection: dorsal motor nucleus of vagus Innervation of cardiac muscle, smooth muscle, and glands of cardiovascular system, respiratory, and gastrointestinal tracts For example, in the stomach, the vagus nerve increases the rate of gastric emptying, and stimulates acid production.
Superior and inferior rectus muscles Superior and inferior oblique muscles
Varies on horizontal position When eyes are abducted- rectus muscles are primary eye movers When eye is adducted- oblique muscles are primary movers Oblique muscles also responsible for torsional movements (turning)
Superior and inferior rectus muscles (both CN III) Superior (trochlear, CN IV) and inferior oblique muscles (CN III)
Vertical movements Elevation due to action of superior rectus and inferior oblique Depression due to action of the inferior rectus and superior oblique
Damage to vestibulocochlear nerve VIII
Vestibular neuritis: inflammation of the vestibular branch of the vestibulocochlear nerve. Some cases are thought to be due to reactivation of the herpes simplex virus. It presents with symptoms of vestibular nerve damage: Vertigo - a false sensation that oneself or the surroundings are spinning or moving. Nystagmus - a repetitive, involuntary to-and-fro oscillation of the eyes. Loss of equilibrium (especially in low light). Nausea and vomiting. The condition is usually self-resolving. Treatment is symptomatic, usually in the form of anti-emetics or vestibular suppressants Tinnitus The perception of chronic tinnitus has also been associated with hyperactivity in the central auditory system, especially in the auditory cortex. In such cases, the tinnitus is thought to be triggered by damage to the cochlea (the peripheral hearing structure) or the vestibulocochlear nerve.
Cranial Nerve VIII
Vestibulocochlear Sensory Innervates vestibular apparatus, cochlea Central connection: vestibular nuclei, cochlear nuclei Vestibular sensation (position and movement of head), hearing The vestibular and cochlear portions of the vestibulocochlear nerve are functionally discrete, and so they originate from different nuclei in the brain: Vestibular component - arises from the vestibular nuclei complex in the pons and medulla. Cochlear component - arises from the ventral and dorsal cochlear nuclei, situated in the inferior cerebellar peduncle. Both sets of fibers combine in the pons to form the vestibulocochlear nerve. The nerve emerges from the brain at the cerebellopontine angle andexitsthe cranium via the internal acoustic meatus of the temporal bone
Medulla
Where spinal cord magically turns into brain around the level of the foramen magnum Emergence of the pyramids and pyramidal decussation The "upper" end of the medulla is about in line with the cerebellar peduncles, where it becomes physically continuous with the pons Cranial Nerves: hypoglossal (XII, motor), vagus (X, mixed), and glossopharyngeal (IX, mixed) Also accessory nerve if you want to lump it in there... Maybe a touch of the facial (solitary nucleus) and trigeminal Solitary nucleus: sensory neurons from 3 different cranial nerves Spinal Trigeminal nucleus: shared by multiple cranial nerves; crude temperature/touch from trigeminal and pain from all 4 Cochlear nucleus: sort of sits on the fence between pons and medulla Cranial Nerves: hypoglossal (XII, motor), vagus (X, mixed), and glossopharyngeal (IX, mixed) Also accessory nerve if you want to lump it in there... Maybe a touch of the facial (solitary nucleus) and trigeminal The abducens (VI, motor), facial (VII, mixed), and vestibulocochlear (VIII, sensory) nerves exit at the pons-medulla junction
Brainstem: Crus cerebri
anterior part of the cerebral peduncle; contains motor tracts coming from the cortex motor tracts; anterior portion of cerebral peduncle; link brainstem to thalamus (cortex)
Brainstem: Interpeduncular fossa
houses oculomotor nucleus Fun fact: exists in primates, but does not appear to exist in rodents
Brainstem: What makes it up (midbrain structures and so on)
midbrain, pons, and medulla Midbrain includes substantia nigra, colliculi, red nucleus, VTA... This is why I generally call the brainstem "the midbrain and stuff" Home of 10 pairs of cranial nerves We know it for role as motor and sensory information highway We love it for role in cardiac and respiratory function
Why striate and extrastriate visual cortices are a critical part of smooth pursuit movements
neurons in the striate and extrastriate visual cortices are supplying essential sensory information Remember- have neurons that selectively respond to motion and orientation
If certain types of movement are voluntary or not
saccades can be both smooth pursuit movements under voluntary you can choose to track something
Foveation
the act of directing the fovea towards new objects of interest
